Nobel Prize in Physics 2023

Pierre Agostini, Ferenc Krausz and Anne L’Huillier receive award for ultra-short pulses of light, which have enabled the close study of electrons.

The 2022 Wolf Prize in Physics has been awarded to Paul Corkum, Anne L’Huillier and Ferenc Krausz for their pioneering contributions to ultrafast laser science. Nature Photonics spoke to them about the milestones, challenges and future opportunities for the field.

Three pioneers of attosecond physics share the 2022 Wolf Prize in Physics.

Attosecond spectroscopy promises real-time observation of the motion of electrons inside atoms. Nadya Anscombe talks to Ferenc Krausz from the Max-Planck Institute of Quantum Optics and the Ludwig-Maximilians-University of Munich in Germany about the technology.

When exposing a tungsten crystal to intense light, the travel times of emitted electrons differ by 110 attoseconds, depending on whether they were originally tightly bound to one atom in the crystal or delocalized over many atoms. This ability to directly probe fundamental aspects of solid-state electron dynamics could aid the further development of modern technologies such as electronics, information processing and photovoltaics.

Seven scientists share their views on some of the latest developments in attosecond science and X-ray free electron lasers (XFELs) and highlight exciting new directions.

Attosecond science is nowadays a well-established research field, and table-top attosecond sources based on high-harmonic generation are routinely used to access electronic motion in matter at its natural time scale. Here, the authors describe a new way of doing chemistry—attochemistry—by directly acting on the electronic motion, and discuss a few key open questions in this emerging field.

Even for simple systems, the interpretations of new attosecond measurements are complicated and provide only a glimpse of their potential. Nonetheless, the lasting impact will be the revelation of how short-time dynamics can determine the electronic properties of more complex systems.

A systematic experimental study of the ionization of argon by mid-infrared light confirms half-a-century-old predictions and paves the way to the development of brighter, shorter attosecond pulse sources.

The discovery of an overlooked but apparently ubiquitous spike in the mid-infrared photoelectron spectra of molecular and atomic gases suggests that we don’t know as much as we thought we did about the ionization of matter in strong fields.

By exploiting the Keldysh scaling — universal wavelength scaling laws in strong-field physics — direct temporal characterization of high-harmonics is demonstrated using sum-frequency-generation cross-correlation frequency-resolved optical gating (SFG XFROG).

High-order harmonic generation is a nonlinear optical process that enables the creation of light pulses at frequencies much higher than that from a seed laser. The host medium for this interaction is typically a gas. Now, the process has been observed in a bulk crystalline solid with important implications for attosecond science.

A solid-state device is demonstrated that can detect the absolute offset between the carrier wave and envelope of an ultrashort pulse, the carrier–envelope phase. It holds promise for routine measurement and monitoring of the carrier–envelope phase in attosecond experimental set-ups.

Frequency combs have revolutionized the study of electronic structures and dynamics of matter but currently used lasers systems are limited in terms of achievable pulse energies. Here, Pronin et al.demonstrate few cycle pulse emission from a thin-disk laser with 150 nJ pulse energy and 7.7 fs pulse duration.

The properties of high harmonic generation from solids are not fully understood. Here, Wang et al. control the photo-carriers injected in a semiconductor to distinguish interband and intraband contributions to different high harmonics, and investigate the wavelength dependence of the harmonics.

Continuously adjustable single-cycle waveform spanning from 0.9 to 12.0 μm is obtained by cascaded intrapulse difference-frequency generation in a ZnGeP₂ crystal. The cascade-associated phase response—distinct for different spectral bands—provides a new tuning parameter for waveform adjustment.

This Expert Recommendation describes how high conversion efficiency in high-order harmonic generation can be achieved over a large range of pressures and medium lengths, following a hyperbolic equation, and provides design guidance for future high-flux extreme ultraviolet sources.

This review discusses significant recent advances in the generation, characterization and application of ultrabroadband isolated attosecond pulses with a spectral bandwidth comparable to the central frequency, which can in principle be compressed to a single optical cycle.

A technique that uses the rotating electric-field vector of a circularly polarized laser pulse as a ‘clock’ provides a fresh approach to measuring electron dynamics with attosecond time resolution.

Time-resolved probing of electronic dynamics such as exciton formation and annihilation requires attosecond pulses at photon energies covering the absorption edges of materials. Here, Silva et al. experimentally demonstrate spatio-temporal isolation of single-attosecond soft X-ray pulses in the water window.

Attosecond soft X-ray pulses hold promise for probing electronic dynamics in real time, but it is challenging to achieve element sensitivity while maintaining temporal resolution. Teichmann et al. report the cover of carbon, nitrogen and oxygen absorption edges with an isolated pulse supporting 13 as duration.

This article reviews the basic concepts underlying attosecond measurement and control techniques. Emphasis is given to exploring the fundamental speed limit of electronic signal processing that employs ultimate-speed electron metrology provided by attosecond technology.

Measurements of the electron wavepackets produced by photoionizing noble gas atoms with an XUV harmonic comb enable the reconstruction of the effective binding potential: a new technique that could be extended to molecules.

To better understand the mechanisms of double ionization following the absorption of one photon, a combination of experimental techniques has been developed to probe the electron emission times in xenon on the attosecond timescale.

An optical-field-driven streak camera for the temporal characterization (with potentially attosecond resolution) of ultrashort free-electron pulses at 25 keV is demonstrated. It involves intersecting an electron beam and a laser beam at a thin metal mirror.

Attosecond streaking is used to study the dynamics of electron scattering in dielectric nanoparticles in real time. Revealing the mechanisms involved is the first step towards understanding electron scattering in more complex dielectrics.

An experiment demonstrating the generation of subfemtosecond pulses of light through the interaction of laser light with a solid target underlines the potential of this approach to lead to a new generation of intense sources of attosecond pulses.

A time-resolved observation of electron tunnelling and the short-lived electronic states that subsequently appear is useful as a new approach to obtain insights in multi-electron dynamics inside atoms and molecules. This technique of 'attosecond tunnelling' is applied to study the cascade of electronic transitions that occur in xenon atoms as a result of their ionization.

A vibrational spectroscopy technique that measures the electric field emitted from organic molecules following infrared illumination allows their molecular fingerprints to be separated from the excitation background, even in complex biological samples.

Attosecond technology (1 as = 10⁻¹⁸ S) promises the tools needed to directly probe electron motion in real time. These authors report attosecond pump–probe measurements that track the movement of valence electrons in krypton ions. This first proof-of-principle demonstration uses a simple system, but the expectation is that attosecond transient absorption spectroscopy will ultimately also reveal the elementary electron motions that underlie the properties of molecules and solid-state materials.

The ultrafast reversibility of changes to the electronic structure and electric polarizability of a dielectric with the electric field of a laser pulse, demonstrated here, offers the potential for petahertz-bandwidth optical signal manipulation.

Attosecond light pulses are now available experimentally, enabling ultrafast processes on the atomic scale to be probed; here the free-electron-like propagation of electrons through ultrathin layers of magnesium is observed in real time.

Intense light pulses in the visible and adjacent spectral ranges with their energy mostly confined to a half wave cycle—optical attosecond pulses—are synthesized and used to measure the time it takes electrons to respond to light.

Petahertz-bandwidth metrology is demonstrated in the measurement of nonlinear polarization in silica.

Attosecond (10⁻¹⁸ s) laser pulses make it possible to peer into the inner workings of atoms and molecules on the electronic timescale — phenomena in solids have already been investigated in this way. Here, an attosecond pump–probe experiment is reported that investigates the ionization and dissociation of hydrogen molecules, illustrating that attosecond techniques can also help explore the prompt charge redistribution and charge localization that accompany photoexcitation processes in molecular systems.

Understanding of photoionization dynamics, one of the fastest processes in nature, requires the characterization of all underlying ionization channels. Here the authors use an interferometry technique based on attosecond pulses to measure the phase and amplitude of the individual angular momentum channels in the photoionization of neon.

Here the authors report experiment and theory study of the photoionization of xenon inner shell 4d electron using attosecond pulses. They have identified two ionization paths - one corresponding to broad giant dipole resonance with short decay time and the other involving spin-flip transitions.

Resonant absorption of light in atoms can lead to autoionization, whose probability exhibits a Fano intensity profile. Here, the authors use attosecond pulses and weak infrared radiation to study the phase variation of the photoionization amplitude across an autoionization resonance in argon.

Ionization time delays are of interest in understanding the photoionization mechanism in atoms and molecules in ultra-short time scales. Here the authors investigate the angular dependence of photoionization time delays in the presence of an autoionizing resonance in argon atom using RABBITT technique.

Though strong-field induced carrier excitation allows for exploring ultrafast electronic properties of a material, characterizing post-excitation dynamics is a challenge. Here, the authors report linear petahertz photoconductive sampling in a solid and use it to real-time probe conduction band electron motion.

Characterization of light pulses is important in order to understand their interaction with matter. Here the authors demonstrate a nonlinear photoconductive sampling method to measure electric field wave-forms in the infrared, visible and ultraviolet spectral ranges.

Photoemission from nanometre-scale structures offer a route toward ultrafast light-field-driven electronic nanocircuits. Here, the authors use attosecond streaking spectroscopy for nanoscale characterization of near-fields in the vicinity of tapered gold nanowires.

Studying the dynamics of electrons is important for understanding fundamental processes in materials. Here the ionization of a pair of electrons in argon atoms is explored on attosecond timescales, offering insight into their correlated emission and the double ionization mechanism.

Direct measurement of the electric field of light in the near-infrared is experimentally demonstrated, showing that careful optical filtering allows the time-resolved detection of electric field oscillations with half-cycle durations as short as 2.1 fs, even with a 5 fs sampling pulse.

A demonstration of attosecond control of the motion and directed emission of electrons from individual silica nanoparticles using few-cycle laser fields opens new possibilities to manipulate electronic processes in nanoscale systems.

Attosecond light pulses are used for ultrahigh-resolution observations of ultrafast phenomena in atoms, molecules and condensed matter. Measuring the durations of such pulses is challenging because the spectrum lies in the vacuum ultraviolet or soft-X-ray range. This article reviews and compares two methods — photoionization and photorecombination — for measuring the duration of attosecond pulses.

Attosecond science allows the role of electronic coherence in the control of chemical reactions in molecular systems to be investigated. This article reviews recent activities in attosecond molecular science and identifies some promising directions for further development.

Ultrafast X-ray spectroscopies enable the investigation of fast chemical dynamics with time resolutions reaching the order of attoseconds. Processes such as spin crossover, structural deformations in excited states and dissociation reactions can now be studied through the use of short X-ray pulses produced by high-harmonic, free-electron-laser and synchrotron sources.

Lightwave electronics could enable the control of interactions in quantum materials and provide access to the quantum phases and quantum information of condensed-matter systems. This Review discusses the fundamental concepts of lightwave electronics and outlines key advances and potential applications.

X-ray free electron lasers provide high brightness sources that permit the study of low-cross section phenomena, such as Compton scattering from atoms and molecules. Here, the angular distribution of electrons after stimulated Compton scattering from molecular hydrogen are simulated, revealing the influence of dipole and non-dipole transitions.